HDBMS Hierarchical Database Management System
A
hierarchical database model is a data model in which the data is organized into
a tree-like structure. The data is stored as records which are connected to one
another through links. A record is a collection of fields, with each field
containing only one value. The entity type of a record defines which fields the
record contains.
1 Example of a hierarchical model
A record
in the hierarchical database model corresponds to a row in the relational database
model and an entity type corresponds to a table.
The
hierarchical database model mandates that each child record has only one
parent, whereas each parent record can have one or more child records. In order
to retrieve data from a hierarchical database the whole tree needs to be
traversed starting from the root node. This model is recognized as the first
database model created by IBM in the 1960s.
The
Hierarchical Data Model is a way of organizing a database with multiple one to
many relationships. The structure is based on the rule that one parent can have
many children but children are allowed only one parent. This structure allows
information to be repeated through the parent child relations created by IBM
and was implemented mainly in their Information Management System.
2 Advantages
The model
allows easy addition and deletion of new information. Data at the top of the
Hierarchy is very fast to access. It was very easy to work with the model
because it worked well with linear type data storage such as tapes. The model
relates very well to natural hierarchies such as assembly plants and employee
organization in corporations. It relates well to anything that works through a
one to many relationships. For example; there is a president with many managers
below them, and those managers have many employees below them, but each
employee has only one manager.
3 Disadvantages
This
model has many issues that hold it back now that we require more sophisticated
relationships. It requires data to be repetitively stored in many different
entities. The database can be very slow when searching for information on the
lower entities. We no longer use linear data storage mediums such as tapes so
that advantage is null. Searching for data requires the DBMS to run through the
entire model from top to bottom until the required information is found, making
queries very slow. Can only model one to many relationships, many to many
relationships are not supported. Clever manipulation of the model is required
to make many to may relationships.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.